Hereinafter, a conventional power conversion device is described with reference to drawings. FIG. 4 is a circuit block diagram of a conventional power conversion device. FIG. 4 is a circuit block diagram showing configurations of power conversion devices 2 and 3 in conventional power supply device 1. Power supply device 1 includes power conversion device 2 and power conversion device 3. Power conversion device 2 and power conversion device 3 have the same configuration except for polarity. Therefore, herein, the configuration and operation are described with respect to power conversion device 3.
Power conversion device 3 includes switch units 4, 5, 6, and 7, gate drive units 8, 9, 10, and 11 corresponding to switch units 4, 5, 6, and 7, and DC power supplies 8P, 9P, 10P, and 11P for supplying the gate drive units with a DC voltage. In particular, when power conversion device 3 is applied to respond to high power, in order to reduce a burden in individual switch units 4, 5, 6, and 7, and in order to respond to a large electric current, switch units 4, 5, 6, and 7 are connected in parallel.
Herein, switch units 4, 5, 6, and 7 are provided with inductive reactance 4A, 5A, 6A, and 7A, respectively. Furthermore, values of voltages generated by transient-state electric currents 14, 15, 16, and 17 flowing into inductive reactance 4A, 5A, 6A, and 7A are different from each other. Thus, values of electric potential of source terminals 4S, 5S, 6S, and 7S of switch units 4, 5, 6, and 7 are also different from each other. Gate drive units 8, 9, 10, and 11 and DC power supplies 8P, 9P, 10P, and 11P are provided corresponding to switch units 4, 5, 6, and 7, respectively. Therefore, a voltage between a gate and a source in each of switch units 4, 5, 6, and 7 is dependent on only a voltage supplied from each of gate drive units 8, 9, 10, and 11. Electric potential values of source terminals 4S, 5S, 6S, and 7S are different by the transient-state electric currents 14, 15, 16, and 17, but the voltage between the gate and the source is hardly affected by source terminals 4S, 5S, 6S, and 7S. Thus, switch units 4, 5, 6, and 7 are driven by individual gate drive units 8, 9, 10, and 11, respectively.
Note here that prior art literatures relating to this application include, for example, PTL 1.